Conventionally, fixed orifices are generally used in pressure-controlled flow controllers, and by using orifices with orifice hole diameters suitable for maximum control flow rates, flow control in a fixed flow rate region is performed.
However, when fixed orifices are used, orifices with different orifice hole diameters have to be prepared corresponding to the maximum control flow rates, and therefore, many kinds of pressure-controlled flow controllers with different flow rate ranges are inevitably prepared, and this poses various problems in reducing manufacturing costs and product management, etc.
On the other hand, in order to avoid the various problems in the above-described fixed orifice type pressure-controlled flow controller, the inventors, et al., of the invention of the present application previously invented a variable orifice type pressure-controlled flow control system shown in FIG. 12 and FIG. 13, and disclosed it in Japanese Patent No. 3586075.
That is, this pressure-controlled flow controller 27 includes a pressure control unit A and a variable orifice unit B, and the pressure control unit A includes a pressure control valve 22, a control valve drive unit 23, a pressure detector 24, and an arithmetic and control device 27a, etc.
Further, the variable orifice unit B includes a direct touch type metal diaphragm valve 25 and an orifice drive unit 26, etc., forming the variable orifice and as shown in FIG. 13, a guide slider 38 and a diaphragm presser 36 are moved down by a stroke L by a pulse motor 34 via a ball screw mechanism 39, and, accordingly, a ring-shaped fluid passage (clearance) between a diaphragm 33 and a valve seat 32b, corresponding to an orifice hole, is adjusted and fixed to a set value.
As a matter of course, the actuation stroke L of the orifice drive unit 26 and the flow rate Q distributed through the fluid passage (clearance) are substantially linearly proportional to one another.
To actuate this pressure-controlled flow controller 27, first, a flow rate setting signal Qs and an orifice opening degree setting signal Qz are input into the control device 27a and a control unit 26a of the orifice drive unit 26. Next, when a gas with a predetermined pressure P1 is supplied to a gas inlet 28a, a pressure detection signal QP1 corresponding to an upstream side pressure P1 detected by the pressure detector 24 is input into the control device 27a, and a flow rate Q=KP1 is computed in the control device 27a. 
Furthermore, from the control device 27a, a control valve control signal Qy corresponding to a difference from the flow rate setting signal Qs is output, and the pressure control valve 22 is controlled to open and close in a direction to reduce the difference between the Qs and Q.
Still further, in order to change the control flow rate range by varying the hole diameter of the variable orifice 25, the setting of the orifice opening degree setting signal Qz is changed. Accordingly, an orifice control signal Qo changes, and as a result, the actuation stroke L of the orifice drive unit 26 changes, and the orifice hole diameter φ changes.
In FIG. 12 and FIG. 13, the reference symbol 29 denotes a thermal type flow meter, 30 denotes a vacuum chamber, 31 denotes a vacuum pump, 40 denotes a coupling, 41 denotes a bearing, 42 denotes a shaft unit, 35 and 37 denote springs, 32b denotes a valve seat, 32 denotes a main body, 32a denotes a gas inlet passage, and 32e denotes a gas outlet passage.
In the pressure-controlled flow controller 27 shown in FIG. 12 and FIG. 13, a direct touch type metal diaphragm valve is used as a variable orifice, and the control flow rate range is switched by changing the actuation stroke L of the diaphragm. Therefore, the structure of the orifice is simplified and sliding portions are completely eliminated, and dust emission is also almost completely eliminated. In addition, the dead space inside the fluid flow passage is significantly reduced, and gaps that cause gas to be involved in the fluid flow passage are eliminated, and gas replaceability is significantly improved. Furthermore, by changing the actuation stroke L of the diaphragm, the orifice hole diameter can be easily and accurately changed (that is, the flow rate range can be changed), and as compared with the conventional case where a fixed orifice is replaced, excellent practical effects, such as a great improvement in control performance can be obtained.
However, many problems that should be solved still remain in the variable orifice type pressure-controlled flow controller shown in FIG. 12 and FIG. 13. Among the problems, in recent years, shortening of the time to be taken to switch the flow control range has particularly become an issue, and shortening of the time required to switch the setting of the variable orifice 25 itself and significant shortening of the lowering time during use of the set variable orifice have been demanded.
That is, the variable orifice 25 (diaphragm valve) is set to have an opening area suitable for the control flow rate by adjusting the clearance between the diaphragm 33 and the valve seat 32b by adjusting the actuation stroke L of the orifice drive unit 26. However, the orifice drive unit 26 is mainly composed of the ball screw mechanism 39, so that a considerable amount of time (approximately 1 to 3 seconds) is required to adjust the clearance of the variable orifice 25 (orifice opening area setting), and switching of the flow control range cannot be swiftly performed.
Flow control after completion of setting (clearance adjustment) of the variable orifice 25 is performed by adjusting the pressure P1 by the pressure control valve 22, however, for example, to lower the control flow rate from the 100% set flow rate (10 sccm (Standard cubic centimeters per minute)) to 20% (2 sccm) by using an orifice for 10 sccm, as shown in FIG. 14, a lowering time of approximately 6 seconds is required. This FIG. 14 is based on an actual measured value of the lowering time from the 100% set flow rate (10 sccm) to the 20% set flow rate (20 sccm) in the case where a fixed orifice with a hole diameter of 18 μm was used as the orifice for 10 sccm, and the fluid passage volume between the pressure control valve 22 and the orifice was set to 0.2 cc.
The lowering time t=6 seconds in this FIG. 14 was actually measured in the case where a fixed orifice with an orifice hole diameter φ=18 μm was used, and it was found that this lowering time t was mainly caused by a gas existing in the fluid passage volume of 0.2 cc on the upstream side of the orifice, and by reducing the fluid passage volume between the pressure control valve 22 and the orifice, and by an increase in the orifice hole diameter, accordingly, the lowering time t could be shortened.